A Decade in Community-Supported Development of the Frequently Updated RAP and HRRR Model Forecast Systems: From Research to Operations and Back Again (WAF Early Career Award)

Community support for hourly-updating numerical weather guidance that included the foundational CONUS-scale Rapid Update Cycle (RUC) model originated with the short-term forecast needs of the aviation industry where both tactical and strategic decision making, on the time scale of hours, resulted from weather impacts on the national airspace system. With increasing high-performance computer (HPC) power and the maturation of national observation networks such as the National Weather Service WSR-88D radar mosaic over the last decade, both the geographic domain and horizontal resolution of the RUC were increased through succession to the respective next-generation Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR) model forecast systems that started development a little more than a decade ago. These new models were designed with community-based components including Gridpoint Statistical Interpolation (GSI) for observational data assimilation, a specially configured version of the Advanced Research WRF (ARW) model, and unified post-processing (UPP).

The increased resolution of HRRR facilitated explicit prediction of deep moist convection including most commonly observed convective modes and increased the utility of these frequently updating forecasts with the severe weather forecasting community where forecasts of the mesoscale environment would be complemented with explicit predictions of convective evolution. More recently, continued growth of computer resources has permitted extension of the RAP and HRRR forecast lengths beyond the “day one” period with upcoming operational forecasts out to at least 36 hours by mid-2018 along with HRRR coverage over Alaska. These forecast extensions have also contributed to increased use by and interaction with both renewable energy and hydrologic communities where decision making and forecast products tend to operate on these longer time scales.

With the adoption of community-supported model components such as GSI, WRF-ARW and UPP and HPC growth, more frequent contributions to the RAP and HRRR development were possible, and as such, a more agile model development paradigm was established with rapid prototyping for evolutionary upgrades to the RAP and HRRR including use of real-time experimental forecasts that permit operational forecaster feedback. This paradigm and close coordination with the National Center for Environmental Prediction (NCEP) Environmental Modeling Center (EMC) has facilitated a two-year research-to-operations (R2O) transition cycle for the RAP/HRRR between their operational inceptions in 2012/14 and present. We are now concluding the third and fourth R2O cycles of the HRRR and RAP respectively with another transition cycle planned for completion by mid-2020. These R2O transitions have also facilitated O2R feedback from NCEP central operations (NCO) to help maximize computational efficiency in the RAP/HRRR.

This presentation will review historical highlights of RAP/HRRR development and include a look towards 2020 and eventual incorporation in a unified forecast system. Highlights will emphasize developmental drivers from various communities in the weather enterprise along with some experiences and lessons learned during the R2O process.